Powdered metal product



Dec. 23, 1941- w. G. CALKINS ETAL I POWDERED METAL PRODUCT Filed Sept. 5, 1940 s WW 6 V Rm R OHEA wauM was IME MY mm w WARD VV- 7% I 1% ATTORNEYS.

screen material.

Patented Dec. 23,1941

UNITED STATE s PATENT OFFICE rowpcaap METAL raon'uor William G. aalkins and Roy E. Blue, Detroit, and Ward W; Marvin, Royal Oak, Mich assignors to Chrysler Corporation, Highland Park, Mlch.,

a corporation of Delaware Application September 5, 1940, Serial No. 355,424

. I Claims.

Our present invention relates to the formation of articles,such as screen material, from comminuted metal.

The principal object of the invention is to provide screen material of any desired shape, con-. tour, mesh, corrosion resistance, or other characteristics, from metals or alloys of metals-by a process comprising comminuting the metals or ground into fine particles and agglomerated by heat may be formed into articles such as screen material. A further advantage of the present invention is that screen material may be formed with reinforcing ribs integrally associated therewith, with binding edges integrally formedthereon, or with fancy shapes, contours and mesh characteristics. irregular meshes, or any other feature desired by the designer of the article or A further object of the present invention is to form screen material of metals or alloys of metals in mesh sizes which could not be achieved by molten molding processes,.and which could only be achieved with considerable difflculty or expense by wire drawing and weaving processes or by drilling or perforating fiat sheets.

A further object of the present invention is to provide a method and apparatus for forming screen material having the above characteristics.

These and other objects and advantages of the present invention maybe realized from an inspection of the accompanying specification and drawing wherein a preferred form of the article and apparatus is illustrated and described and wherein preferred methods of operation are schematically illustrated and described.

In the drawing, wherein like numerals refer to like parts throughout, Fig. l is a view in perspece tlve of a portion of a mold for forming screen material in accordance with the present invention;

Fig. 2 illustrates a step in the operation of forming an article, such as screen material, in accordance with the herein disclosed process and using the mold illustrated in Fig. 1;

' material in'the mold;

in disclosed showing a furnace for sintering the Fig. 5 discloses an article, such as screen material, formed by the present process and apparatus; and, v

Fig. 6 is a sectional view taken substantially along lined-6 of Fig. 5.

In accordance with our invention we may use any comminuted metal. or alloy, such as copper,

bronze, brass, nickel, chromium, Monel metal,

iron, or any other suitable or desired metal or alloy which is capable of being ground or com,-

minuted in any known manner to a particle size sufficiently smaller than the smallest dimensions of the article to be formed in order that the particles may be compacted into grooves or depressions conforming to the article to be formed. For

example, 90% copper in comminuted form may be mixed with 10% tin in comminute'd form; or

proportion of basic metals in alloyed form. It is.

only necessary that a metal of high melting point constitute the major proportion of the metal Fig. 3 illustrates a further step in the process herein disclosed, showing a portion of a press of utility in accordance with the present disclosure;

Fig. 4 shows a further step in the process herepresent so that the comminuted particles may be sintered at a temperature below the melting point of the metal forming the major proportion of the mass and above the melting point of the metal, or metals, forming the minor proportion of the mass in order that the metal of low melting point may flow around and between the particles of metal of high melting point to sinter the mass into a self-sustaining structure. for which the metal of high melting point provides the structural strength and other properties desired. In this regard the metal of low melting point may be tin which would bond together particles of copper or'some other metal having a higher melting point, the tin also providing a surface coating for resistance against corrosion; or. the metal of low melting point may be copper which would flow around and between particles of a metal of higher melting point, such as iron, to bond the iron particles together and to protect the same from rust and other forms of corrosion. It may be desirable to first alloy the metals in the desired proportion, then to grind or otherwise comminute the alloy, and then to sinter the comminuted alloy particles so that some of the metal of low melting point would sweat out of the alloy sufliciently to form bonding contact with other particles in the mass of material, in which case the articles would com- 2 prise principally the alloyed metals in a state of alloy having desired properties not obtainable with the use of mixtures of the same metals.

As seen in the drawing, a mold may be provided by shaping a surface ll) of a block of material I I, the mold being formed from a substance which is infusible at the temperatures necessary to sinter the comminuted particles. The substance from which the mold is formed may comprise any of such materials as graphite, stainless steel, ceramic material, or cold rolled steel having a chromium oxide surface protection thereon. The mold is machined or otherwise shaped to conform to the contours of the desired article, they mold in Fig. 1 being shaped to provide intersecting grooves i2 and an edge depression it. In the illustration, the grooves i2 conform tothe shape and mesh size of screen material desired and the edge depression forms a square head or edge trim around the screen integrally united with the mesh of the screen..

In performing the process of .iorming articles the depressions in the surface of the mold are filled by heaping a mass of the comminuted material on top of the mold and removing the etacess material extending above the depressions in the mold, as by means of moving a straightedge across a plane surface mold or by otherwise striking off the excess material extending above the mold. The mold with the material in the depressions therein is then placed in a press as shown in Fig. 3 comprising a bed IS on which the mold is placed and a ram il comprising a platen I8 of rubber, or other rubberous material such as chloroprene or Buna rubber, placed in a depression IS in the ram which is shaped to fit over the edge of the mold. The rubberous material is preferably sufficiently resilient to flow into the depressions of the mold and compress the comminuted particles into intimate contact with each other, but of suflicient surface strength not to be ruptured or punctured by the comminuted particles. If necessary or desirable, the mold may be removed after compression of the mass of comminuted particles and the steps of placing a mass of comminuted material thereon, removing the excess material therefrom and compressing the material in the depressions may be repeated until the material has been built up in the depressions to the desired depth .or thickness.

In order to aid in the compression of the particles into a closely knit mass of particles, it is sometimes desirable to add a small proportion of a dry lubricant, such as powdered boric acid, graphite powder, exfoliated vermiculite, or any other dry substance which aids in causing the particles to slide past one another and which is preferably incapable of detracting from the alloy characteristics or the bonding strength of themetals when the mass is sintered. Such a dry lubricant should be added in amounts of from to l A9 of the comminuted metal.

-After sufficient powdered material has been compacted into the depressions of the mold, the mold is placed in' an oven having a non-oxidizing atmosphere maintained therein at a sintering temperature. The atmosphere may be a reducing atmosphere such as hydrogen, or it may be an inert atmosphere such as ordinary illuminating gas.

The sintering operation is preferably conducted at a temperature between the melting points of the metals of higher and lower melting points. For example, a mixture of copper and tin may be sintered at an atmosphere of 1600' F. to 1650 F., the melting point oi. commercially pure copper being 1981 F. and the melting point of commercially pure tin being 415 F vThe sintering operation is maintained at the stated temperature long enough for the tin to be melted and to flow between the particles of copper'to bond the same together and protect the surfaces thereof. In an iron and copper mixture a temperature between the melting point of copper and the melting point of iron, such as 2200 F. to 2500 F. may be maintained sumciently long enough to cause the copper to flow between the particles of iron. If an alloy is comminuted and sintered in the mold the temperature is preferably maintained at a temperature below the. melting point of the alloy but above temperature ispreferably maintained in the neighborhood of'1600 to 1650" F., which. considerably belowthe melting point of the al loy but sufiiciently above the melting point oi the tin in the alloy to cause some of the tin to sweat out of the alloy and bond the alloy particles together. maintained at any temperature above the melting point ofthe'metal of-low melting point and below the melting point of themetal -of high melting point but preferably should be maintained at a temperature closer to the melting point of the metal of high melting point so that the sintering operation may be more rapidly performed.

An unexpected result of the foregoing process is that very fine mesh screen material formed from particles compacted in an open groove would be expected to have a completely flat surface contour, whereas the fact is that the compressing and sintering operations cause the mesh strand portions to assume a cylindrical or nearly cylindrical shape. An advantage of the foregoingprocess is that very large sheets of fine mesh screen material may be formed whereas molten molding processes even when conducted at high temperatures and very high pressures are limited not only as to the size of sheet formed but also as to the mesh size since the molten metal would cool before completely filling the mold.

In the sintering process the dry lubricant powder may decompose or vaporize at the sintering temperature, as would be the case with boric acid which melts at 365 F. with some decomposition and boils at 572 F. giving off water of crystallization and further decomposing. On the other hand, graphite powder has a meltingpoint of substantially 6380 F. and would not be affected by the sintering heat so that the fine graphite particles would be maintained in the sintered mass of metal particles. Such would be the case with exfoliated vermiculite as well.

While we have illustrated and described only preferred embodiments of the presentinvention, it can be appreciated by those skilled in the art that various combinations of materials may be used,.that various modifications of the process may be used, and that the apparatus used to perform the process may take various embodiments. All such as come within the scope of The vsintering oven may be the following claims are considered to be a part of our invention.

We claim:

1. The method of making metallic screen material comprising providing a block of material unafiected by temperatures capable of sintering the metal from whichthe screen material, is made with depressions conforming to the mesh 01'' the screen material, intimately associating comminuted metallic particles with a dry lubricating powder chosen from the class of materials represented by graphite, exfoliated vermiculite and boric acid in the proportion of substantially 98 metal to l dry lubricant, heaping a mass of the mixture on the shaped surface of the block, striking off the excess mix- I ture, compressing the mixture into the depressions, and sintering the mixture in a non-oxidizing atmosphere. I

2. The method of making metallic screen material comprising comminuting a metal of a high melting point and a metal of a low melting point, associating the comminuted metals intimately into a mixture consisting of a major proportion of the metal of high melting point, adding to the mixture a small proportion of powdered dry lubricant such as graphite exfoliated vermiculite, or boric acid, heaping a mass of the final mixture of metals and dry lubricant on the grooved surface of a mold, striking off the excess mixture above the grooves, compressing the material remaining in the grooves, repeating the operations of'heaping the mixture on the grooved surface, striking oil the excess, and compressing the material remaining in the grooves until the compressed mixture in the grooves is of the desired thickness, and sintering the material in the grooves of the mold in an oven having a non-oxidizing atmosphere therein maintained at a temperature between the melting points of the two metals.

3. The method of making fine-mesh metallic screen material comprising grooving a plane surface of a substantially infusible block in the shape of the screen material desired, comminuting an alloy of a metal of high melting point and structural strength having a relatively small proportion of metal of low melting point alloyed therewith to an extent such that the particles of comminuted alloy are materially smaller in diameter than the dimensions of the grooves in the block, intimately associating with the comminuted alloy particles of dry powdered material such as graphite or the like, spreading the material over the surface of the block so as to fill the grooves of the block with such comminuted material, removing the excess material from the surface of the block, compressing the comminuted material in the grooves of the block, and sintering the material in anon-oxidizing atmosphere at a temperature below the melting point of the alloy but above the melting point of the metal of low melting point in the alloy.

4. Apparatus for forming screen material by sintering comminuted metal in a mold shaped to form such screen material comprising a mold of a substance infusible at a temperature c a-.

pable of sintering the materialof which the screen is made and having grooves in a surface thereof shaped to conform to the desired shape of screen material, and a press for compressing thecomminuted metal into the grooves of the mold comprising a rubberous platen and means to efiect relative movement between the grooved surface of the mold and said rubberous platen so as to compress the comminuted material into the grooves of the mold.

5. The method of making metallic screen material comprising providing a, block of material unaffected by temperatures capable of sintering the metal from whichthe screen material is made with depressions conforming to the mesh of the screen material, intimately associating comminuted metallic particles with a dry lubricating powder chosen from the class of materials represented by graphite, exfoliated vermiculite and ibOIiC acid in the proportion of substantially 98 metal to l /z% dry lubricant, heaping a mass of the mixture on the shaped surface of .the block, removing the excess material from ture in a non-oxidizing atmosphere.

WILLIAM G. CALKINS. ROY E. BLUE. WARD W. MARVIN. 

